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- [Narrator] So here is a
picture of the human heart.

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Now you notice, you see
there's the reddish tinges.

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Those are muscle.

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But all of that off-whitish color

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you're seeing toward the top of it,

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that's all fat, believe it or not.

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Now a typical person is going to

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have fat around their heart.

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It's perfectly natural.

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So this is your heart
and what it looks like

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if it were outside of your body.

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So we look at the heart as
an artistic drawing here.

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What we've done is taken the heart

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and cut the front of it away.

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So you're looking inside
from the front of the body.

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You have that interventricular septum.

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It's the structure in between
the two chambers' lower heart.

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We then have three different
layers of the heart,

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epicardium, myocardium, endocardium.

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Well endo,

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E-N-D-O, means inside.

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So endocardium, inside the heart.

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That's the layering that the blood

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will come into contact with.

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While the myocardium, myo meaning muscle,

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is the muscle of the heart.

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Almost the entire thickness of the wall

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you can see is muscle.

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That's your cardiac muscle.

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Then the epicardium. E-P-I,
epi means outside or around.

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Epicardium is the ouside
layer of the heart,

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helping it keep things
closed and contained.

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So if you start with how the
blood gets back to the heart,

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with the two vena cava.

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The superior vena cava
and inferior vena cava.

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The superios vena cava drains blood

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from your head, your shoulders, your arms.

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While the inferior vena cava is going to

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drain blood from your legs and your torso.

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It enters into the chamber
called the right atrium.

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From there, the blood
goes down through this

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right atrioventricular
valve, or right AV valve,

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into the right ventricle.

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Now that right AV valve,

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you might of heard of
it as a tricuspid valve.

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It has two different
names, either one works.

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So right AV valve or tricuspid valve.

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Once you're in the right ventricle,

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it's time to pump that
blood out of the heart.

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But both the right atrium
and right ventricle

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are oxygen-poor blood.

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If you're leaving the
heart now, we're you going?

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Well you need to pick up oxygen.

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You're heading to the lungs.

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Through the pulmonary valve,
or pulmonary semilunar valve,

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up through the pulmonary trunk and

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the right/left pulmonary artery.

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And that is not a typo,
that is a blue artery.

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Because you remember, the arteries

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carry blood away from the heart.

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And this case, what we're carrying away

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just happens to be the low oxygen.

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It's going to the lungs.

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Once you reach the lungs,
you pick up some oxygen.

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You come back in the left and
the right pulmonary veins.

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And yes, these are going to be red veins.

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They enter back in the left atrium,

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which will then send the
blood down through the

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left atrioventricular valve,

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which is anchored in place
by the chordae tendineae.

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Those little strings or chords

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helps to hold the valve in place.

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And those chordae tendineae are

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anchored by the papillary muscles.

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Now I know I mentioned this
over here in the left ventricle,

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but, the right ventricle
has the same structures.

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The right ventricle still
has the chordae tendineae,

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it still has the papillary muscles.

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But the difference between
the right and left AV valves

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are how many flaps they
have, how many openings.

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The right AV is known as the tricuspid,

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three flaps to the valve.

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While the left AV is called the bicuspid,

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meaning two flaps.

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Or maybe you heard of
it as the mitral valve.

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There's a lot of different
terminology of what it could be.

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So pick one, any one is fine.

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But left AV is usually the
simplest to remember there.

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Once this left ventricle,
with the oxygen-rich blood

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is ready to go, it pumps
out the aortic semilunar.

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Up to the aorta and to
the rest of the body.

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Either it goes up those
three vessels up top,

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going to the head or neck and arms.

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Or it heads down the large
aorta to the trunk and legs.

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So what's around this heart?

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We have the pericardium.

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This fibrous sack that's
meant to hold the heart in

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and prevent it from over filling.

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We already said the three layers:

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epicardium, myocardium, endocardium.

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Remember the epicardium is the outside,

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mostly connective tissue.

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Myocardium is all that cardiac muscle.

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Endocardium is the epithelial,

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nice and smooth and thick.

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So how about these chambers?

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We've mentioned atrioventricles.

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Well we have two atria,
a right and left atria.

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They're more towards the top,

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or superior, part of the heart.

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We'll have two ventricles.

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They're more powerful
because the ventricles

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are what pump the blood out of the heart.

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We have four valves. Valves
are meant to prevent backflow.

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We have the right and left
atrioventricular valves,

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which if you notice I've
put the other names up here.

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So the right atrioventricular

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can become also the tricuspid valve.

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Either of them works.

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The left atrioventricular is also

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known as the bicuspid
valve, or the mitral valve.

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And then we have these
two semilunar valves.

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The pulmonary valve and the aortic valve.

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They're named for where
the blood is going.

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Pulmonary valve is going
to the pulmonary trunk

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and to the lungs, which are referred

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to as your pulmonary circuit.

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While the aortic valve allows blood

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to pass through into the aorta.

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Hence the name, aortic valve.

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So here are these two circuits.

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I said that whole thing is one

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closed process you can't change.

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The two circuits are the
systemic and pulmonary circuits.

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Lets look in the middle in
that lightly shaded box.

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You can the heart, you can see both lungs.

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When the blood leaves the
right side of the heart,

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the right ventricle, it pumps out the

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pulmonary trunk and pulmonary
arteries into the lungs.

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It goes through gas exchange.

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It comes back into the lungs
via the pulmonary veins

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into the left atria.

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That circuit going out of the
heart and back to the heart

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is called the pulmonary circuit.

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But once that nice
oxygen-rich blood is picked up

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it goes down to that left ventricle,

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which is going to pump it out

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either up to your head and arms

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or down to your torso and legs.

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But either way, it's one complete circuit.

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Now this pulmonary circuit

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is going to have several different steps.

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But it must start with the
blood getting back to the heart.

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This is the oxygen-poor blood.

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So its coming back in to the superior and

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inferior vena cava into the right atrium.

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For the right atrium, it
goes to that right AV valve

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into the right ventricle.

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The right ventricle is
going to pump through

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the pulmonary semilunar valve
into the pulmonary trunks.

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The pulmonary trunk with the

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pulmonary arteries head to the lungs.

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From the lungs, you come back
in with oxygen-rich blood

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through the pulmonary veins

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into the left atrium.

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Through the left atrioventricular

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valve to the left ventricle.

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You've now completed
your pulmonary circuit.

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Taking that oxygen-poor blood
when it entered the heart,

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moving to the lungs, picking up oxygen,

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dropping of carbon dioxide.

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Going back to the heart
in the left side now,

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getting down to the left ventricle.

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Well once you leave left ventricle,

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now you're in the systemic circuit.

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It's how you get oxygen delivered
to the rest of your body.

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They travel from the left ventricle

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through the aortic semilunar
valve, to the aorta.

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From here, the aorta starts branching

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and branching into
arteries and arterioles.

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The further you get down the branching,

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the smaller the vessels get.

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Once you pass the arterioles,
you're in the capillaries.

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The capillaries of your body's tissues.

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The capillaries then start to return the

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now oxygen-poor blood back into venules

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and eventually back into veins.

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Because once this oxygen-rich blood

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goes into the capillaries,

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you have gas exchange.

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The capillaries will allow oxygen to

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diffuse out into the tissues.

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It'll also allow carbon dioxide
to come back into the blood.

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So we've started this return trip,

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venules to to veins,
eventually the vena cava,

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into the right atrium.

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Well, we're back. That's it.

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From leaving the heart to
returning to the heart.

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Now it's time for that blood to go

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into the pulmonary circuit again.

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So here's just a little pictorial
view of what is going on.

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As you follow it through,

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the blue is trying to show oxygen-poor.

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The red is oxygen-rich.

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You can notice that
once you come in through

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the superior/inferior vena cava,

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you go right atrium, right
ventricle, pulmonary trunk,

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capillaries, the lungs.

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It comes back into the left
atria, the left ventricle,

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out the aorta and into the
systemic capillaries of the body.

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So one big continuous circle.

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The blood should never stop moving.

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It should constantly keep
moving throughout this process.